This invention relates to hot-melt adhesives for fibers, and in particular relates to hot-melt adhesives made from specified copolyamides. Hot-melt adhesives are used for covering articles of various types, for instance. Such adhesives may be furthermore used as a binder layer for two different materials which have to be bonded together within only a short period of time. Especially, hot-melt adhesives are useful for bonding at least two different fabrics, allowing the usual sewing step to be omitted.
In general, the adhesion process is carried out in such a manner that the hot-melt adhesives are inserted in the form of a powder, emulsion, fiber, or film between the fabrics, and the resulting composite is heated to a temperature at which the hot-melt adhesives are melted, and pressed. Hot-melt adhesives for fibers are usually composed of synthetic polymers. Synthetic polymers composing hot-melt adhesives are required to have a relatively low melting point e.g. 100.degree.-130.degree.C. When the melting point of the synthetic polymer is too high, the step of heating and pressing in the adhesion process has to be carried out at a high temperature, and therefor the fabrics themselves tend to be deteriorated by heating. On the other hand, when the melting point of the synthetic polymer is too low, too much synthetic polymer is infiltrated into the interior of the fabrics during a step of heating and pressing which results in rendering the touch of the fabrics hard and making it difficult to obtain a high adhesive strength, because the infiltrated synthetic polymer does not function as an adhesive agent for the fabrics.
Furthermore, synthetic polymers composing hot-melt adhesives are required to have strong adhesive power.
Heretofore, thermoplastic polymers such as polyethylene, ethylene-vinyl-acetate copolymer, ethylene-ethylacrylate copolymer, polyvinylacetate, polyvinylbutyral, and polyamide have been used for hot-melt adhesives. In particular, copolyamides as described in U.S. Pat. No. 3,515,702 have been most preferably used. This patent teaches the use of hot-melt adhesives consisting essentially of a copolyamide of:
A. laurolactam and; PA1 B. a co-condensible member selected from the group consisting of caprolactam, hexamethylene diamine adipate, hexamethylene diamine sebacate, and mixtures thereof;
In which copolyamide the weight percent of units derived from laurolactam is from 80 % to 20 % and the weight percent of units derived from the co-condensible member is from 20 % to 80 %.
However, according to the teachings of this patent, superior hot-melt adhesives consisting of copolyamides having a melting point within the range of 100.degree.-130.degree.C and having a strong adhesive power cannot be necessarily obtained.
Furthermore, hot-melt adhesives of this patent are very expensive because a high content of the more expensive laurolactam has to be used for obtaining the desired copolyamide.
Accordingly, the first object of present invention is to provide hot-melt adhesives consisting of copolyamides having a melting point within range of 100.degree.-130.degree.C, and having strong adhesive power, at a relatively low cost.
On the other hand, when conventional hot-melt adhesives of copolyamides are used for manufacturing clothing of thin cloth, such as summer wear, there is the serious disadvantage that the clothing has poor appearence because the light which penetrates through the thin cloth is reflected on the surface of the bonding layer consisting of the hot-melt adhesives.
Hot-melt adhesives are very frequently applied for making clothing for suits by bonding a core cloth and a right-side or outer cloth. In this case, conventional hot-melt adhesives cannot provide clothing for suits of good appearence because of the disadvantage mentioned above.
Heretofore, the step of adding conventional delustrants to hot-melt adhesives has been proposed for eliminating this disadvantage. This method is undesirable because it renders the adhesive power of the hot-melt adhesives poor.
Accordingly, the second object of present invention is to obtain hot-melt adhesives which make it possible to provide clothing for summer wear with good appearence. Other objects and advantages of present invention will become further apparent hereinafter.